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Calibration And Electrical Safety Status Of Therapeutic
Ultrasound Utilized By Chiropractic Physicians

By: Dwain M. Daniel, D.C., Ronald L. Rupert, M.S., D.C.

Tel: (972) 294-0848
Email: Dr. Daniel

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Background: Although over 70% of chiropractic physicians utilize ultrasonic therapy (UST), there has never been an investigation of the calibration or electrical safety of this commonly used therapeutic modality within the chiropractic profession. Previous studies of ultrasound units used by physical therapists have been performed in Scotland and Canada. Results of those investigations showed that approximately 2/3�s of units tested did not conform to minimum calibration standards. Similar failure rates may exist in the chiropractic profession and need to be addressed.

Objective: This study sought to determine whether ultrasound machines utilized by chiropractic physicians met established calibration and electrical safety standards and to assess frequency of UST utilization. Secondary objectives were to determine the relative value each physician applied to their training in the utilization of UST and determine correlations between physician�s education, years in practice, gender and proper maintenance of their equipment.

Design: This cross sectional study tested 45 ultrasound units for ultrasonic output, maximum ground resistance and maximum case leakage. A qualified biomedical technician performed the testing using Bio-Tek Instruments Model UW-4 power wattmeter and a Model 175 safety analyzer. Standards established by the Food and Drug Administration and the Association for the Advancement of Medical Instrumentation were followed. Additionally the doctor was asked to complete a short survey relating to education, usage and maintenance of their ultrasound equipment.

Results: 72.1% of doctors contacted used therapeutic ultrasound in their offices. Of the 45 machines tested 44% failed either calibration and/or electrical safety inspection. Failure rate was age dependent (p. 05). Machines that were 5 years old or newer had a combined failure rate of 16.7% while machines over 15 years old had a failure rate 100%. Of the 45 machines tested, only 2 had been safety checked within the last year. Lack regular maintenance of equipment, except for one doctor, rendered secondary correlations between education, years in practice, gender and maintenance of equipment meaningless.

Conclusions: Although the failure rate in the offices visited was less than the failure rate shown in previous studies in physical therapy clinics, there is still a large percentage of machines that are delivering to much or to little dosage to the patient. Electrical safety inspections revealed a smaller but significant failure rate. This study identifies a need for additional educational emphasis on the safety and calibration standards for therapeutic equipment. Chiropractic physicians must become more aware of the requirement for yearly calibration and safety inspections and to understand that failure to maintain their equipment could result in loss in effectiveness of therapy as well as pose a threat to the safety of their patients and staff.

Key Indexing Terms: Chiropractic, ultrasonic therapy, standards, equipment safety, physicians practice patterns, risk management

Introduction: The maturity of a profession can often be measured by its willingness to examine itself. This investigation is such a self-examination.

In 1998 70.3% of all chiropractic physicians utilized ultrasonic therapy (UST) as part of their therapeutic regime and 34.3% of patients seen by these doctors received UST as a component of their office visit (1). This is a small increase from 1991 when 68.8% of all chiropractic physicians utilized UST in their practices (2). A conservative estimate, based on these statistics, suggest there are over 1 million applications of UST performed in chiropractic offices weekly. Due to the wide spread use of UST, the safety and accuracy of these units should be of great concern to the profession.

Previous studies performed in Canada in 1987 (3) and Scotland in 1992 (4) to determine the performance of ultrasound devices demonstrated 66% and 69% respectively of the units tested did not comply with minimum performance standards. Considering the minimum calibration standard for power output is +/- 20% of the indicated output (5), this failure rate is quite alarming. In these studies patients had a better chance of receiving an unprescribed dosage of UST than the prescribed dose. The results of inaccurate dosage can be significant. Since one of the properties of UST is its thermal effect, higher dosages can cause tissue damage. At lower dosages the value of the therapy may be only in it�s placebo effect.

The question must also be raised whether the ultrasound instrument presents an electrical safety hazard to the operator or the patient in the chiropractic office. This issue has not been addressed in previous studies and is included in this study.

The purpose of this study was to assess the electrical safety compliance and calibration accuracy of ultrasound machines in chiropractic physician�s offices and to determine utilization of UST in chiropractic offices. Secondary objectives were to determine the relative value each physician placed on different sources of training in the use of UST and to determine if years in practice, educational background and gender of the doctor are related to calibration and safety.

Materials and Methods: This cross sectional study was accomplished by selecting all chiropractic physicians listed by name in the San Antonio and Dallas, Texas yellow pages. Of the 89 doctors listed, 31 agreed to participate in the study. The balance of the doctors did not utilize UST (13.5%), refused to participate (7%) or were unable to be contacted by telephone (45 %). Each office was visited and the ultrasound units were tested for ultrasonic output, maximum electrical case leakage and maximum electrical ground resistance. A qualified biomedical technician with five years experience in calibration and safety inspections performed the testing. Tests were performed using a new Bio-Tek Instruments Model UW-4 power wattmeter and a new Model 175 safety analyzer. Procedures specified in the operator�s manuals provided by the manufacturer were closely followed (6, 7). All calibrations were performed using deionized, distilled, degassed water. Both units were calibrated by Bio-Tek Instruments at their facility prior to shipment to the principal investigator. Additionally the power wattmeter had regular self-calibration checks performed while in the field. Regulations established by the Food and Drug Administration were used as the standard for ultrasonic power output. This standard states �the error in the indication of the temporal-average ultrasonic power shall not exceed +/- 20% for all emissions� (5). Four separate power settings were tested on each unit. When units were equipped with additional soundheads those soundheads were tested as well. Units that had multiple frequencies available were tested on all frequencies. A total of 214 separate calibration tests were performed on these units, when combining different frequencies and soundheads. Electrical safety standards established by the Association for the Advancement of Medical Instrumentation were utilized (8). Electrical safety tests that were performed were chassis grounding resistance and chassis leakage currents. Chassis leakage currents were measured in normal and reverse polarity, neutral open and closed and with the ultrasound unit turned on and off. The maximum case leakage allowable utilizing these standards is 100 microamperes and the maximum ground resistance allowable is 500 milliohms (8).

In addition to testing of equipment, participating doctors were asked to complete a short survey relating to usage and maintenance of equipment and give a self assessment of the relative value of different educational methods relating to their training in the use of UST.

Data was entered into SPSS for Windows, Version 7.5 for analysis.

Results: 72.1% of the doctors successfully contacted used UST in their offices and 21.8% of those doctor�s patients received UST as a regular part of their treatment regime. These figures are similar to previously reported data provided by the National Board of Chiropractic Examiners as shown in Figure 1 (1).

Of the 45 units tested 37.8% failed to meet the minimum calibration standards and 15.5% failed to pass the electrical safety inspection. The total combined failure rate was 44%. A significant relationship exists between the age of the ultrasound unit and the failure rate (p .05). As shown in Figure 2, units that were 5 years old or newer, 26.7% of the total, had the lowest combined failure rate of 16.7%. Those 6 to 10 years old, 31.1% of the total, had a combined failure rate of 42.9% and those 11 to 15 years old, 24.4% of the total, had a combined failure rate of 37.7%. Those machines over 15 years old, 17.8% of the total had a combined failure rate of 100%. Failure rate of the electrical safety inspection was 5.6% in the units less than 15 years old and 55.6% in units over 15 years old.

On units that failed calibration checks due to low power output at the 5 watts level, the average was 65.6% under the indicated output. On units that failed due do to high power output at the 5 watts level, the average was 42% higher than indicated. This means, on the failed units, a power setting of 5 watts had an average actual output between 1.72 watts and 7.1 watts. Failure at the 5 watts setting, a very common therapeutic dosage, occurred in 1/3 of the units tested. Of the units tested 37% failed due to high output and 63% failed due to low output. Five units had no power output at all at the lowest tested power setting.

Although manufacturers universally recommend yearly calibration checks and safety inspections only 2 of the 45 units tested had been inspected within the last 12 months. 30 units or 66% had never been inspected. With the exception of one doctor who had his equipment inspected on a yearly basis, all other testing, when accomplished, was performed only when the equipment had been serviced for repair.

Table 1 gives a listing of manufacturer�s of the units tested. The failure rate by manufacturer�s range from 14.3% to 100%. Statistical significance between manufacturer and failure rate was not established.

Doctors were asked to rate, on a five point Leikert scale, the value of chiropractic education, post graduate education, manufacturer�s representatives, operator�s manual and self education in their training for the use of UST. As expected doctors rated their chiropractic college as the best source of training (3.48) but surprisingly rated self -education (3.23) a close second. Post graduate education (3.17), the operator�s manual (2.78) and company representative (2.25) followed in order of value.

Since only one doctor had his equipment tested on a yearly basis, there was insufficient evidence to correlate between the doctor�s gender, school, age or years in practice and compliance with recommended maintenance.

Discussion: This is the first study to be conducted within the chiropractic community to evaluate the performance and electrical safety of one of the professions most commonly used therapeutic tools, therapeutic ultrasound.

UST is an electromechanical device that utilizes an electrical current to cause vibration of a crystal to produce high frequency sound waves. Due to these properties it is more susceptible to loss of calibration than other physiotherapeutic devices such as electrical muscle stimulation or shortwave diathermy. Additionally constant motion of the soundhead during treatment can result in metal fatigue and ultimate failure of the cable leading to the soundhead. For these reasons all manufacturers recommend yearly calibration checks of ultrasonic devices to insure accuracy of output. Manufacturers also recommend yearly safety inspections due to the inherent danger of electrical current.

The need for regular calibrations of ultrasound equipment is two-fold. If the actual output is less than the indicated output, the patient may be receiving nothing more than a placebo. 63% of failures in this study were due to low output. 11.1% of the units tested had no power output in the most commonly used therapeutic range, even when indicating output. Secondly, due to its thermal effects, outputs higher than indicated can cause tissue damage. 37% of failures in this study were due to excessive output.

Safety factors are also a concern since improperly grounded or equipment leaking current to the chassis can lead to a shock hazard to the operator or the patient. The National Chiropractic Mutual Insurance Company reports that 3.7% of malpractice claims are related to burns to patients, many of which can be caused by the application of UST or electrical safety issues. (9)

Most chiropractic colleges offer courses in therapeutic modalities both to the undergraduate and graduate doctor. Most states require passage of the physical therapy portion of the National Boards prior to licensure. Consequently it is surprising that only 1 doctor of 31 was aware of yearly inspections recommended by the manufacturer and complied with those guidelines. Reasons for noncompliance could range from other financial priorities within the practice setting, lack of knowledge of the relatively common dangers posed by untested equipment to simple lack of organization within the practice. Based on the findings of this study there appears to be a need for increased emphasis relating to the importance of regular inspections of all therapeutic equipment within the profession. This emphasis should begin in the undergraduate courses taught in chiropractic colleges and extended to postgraduate studies. If increased awareness fails to correct this problem, it may be necessary for regulatory control such as exists with radiographic equipment.

Results of testing show a decrease in the failure rates compared to previous studies performed in Scotland and Canada. However, before concluding that procedures utilized by chiropractic physicians to insure accuracy and safety of therapeutic ultrasound are superior to other professions, other factors should be considered. Detailed, comprehensive testing of an ultrasound machine can take up to four hours. This study only included output checks in continuos mode, case leakage and ground resistance. This was done to minimize downtime for doctors in the study in order increase their interest in participating in the study. Other tests that could have been performed, if time and other resources were available, were effective radiating area of the treatment head, output in the pulsed mode, accuracy of the output frequency and the accuracy of the timer. Higher failure rates in previous studies reflect, at least in part, more detailed examination of the units tested. However, there was a still a marked improvement in chiropractic UST when only comparing the failure rate of continuos output. This is an indicator of improvements in materials and design of units, particularly the presence of solid state circuitry in the newer units tested, rather than superior maintenance and testing of units within the chiropractic community.

The Scotland study showed an increased failure rate in units with multiple frequency soundheads (4). This study did not show a similar pattern. Of the units tested four were multiple frequency and none failed calibration testing. These were newer units, less than five years old, and may account for their accuracy.

It should be noted that the 1987 Canadian study also showed, after the 66% initial failure rate, 62% of the machines had to be recalibrated at least two times over the period of the 44-week study (3). This indicates that the yearly calibration checks are an absolute minimum and biannual checks would be more responsible.

The calibration failure rate for machines over 15 years old, 17.8% of the total tested, was of particular concern. Electrical safety inspection failures reveal a smaller but significant failure rate. Again with machines over 15 years old failing at a much higher rate. Clearly there is a need for chiropractic physicians to become more aware of the necessity for routine calibration and safety inspections of their ultrasound equipment. Older machines should be replaced or thoroughly tested prior to use. All ultrasound machines should be checked for calibration and electrical safety on the minimum of a yearly basis. Failure to do so could lead to serious consequences for the patient and the doctor.

Of the units that failed the electrical safety inspection in this study, most were older units that were not designed to comply with modern case leakage requirements or had corroded ground plugs, which increase resistance. Interestingly one unit failed because the office outlet had been wired incorrectly, creating a hazard. This points out the need to have outlets checked as well as the machines. A new machine in an improperly wired office is just as dangerous as an older machine in the same office. Wiring mistakes can be made just as easily today in a new office as in an office wired 20 years ago. Wiring of the outlets should be checked in all offices.

A weakness in the design of this study was the manner of selection of participants. Only doctors who had their names listed in the yellow pages were selected. This procedure was chosen for the ease in determining whether the doctor was in active practice. It was also used so the doctor could be asked for by name on the telephone, thereby increasing the chance of talking to the doctor and soliciting his or her participation. Even this personal contact met with disappointing results when many receptionists would only take messages and the doctor would not return the call. Combining this problem with the number of doctors that had closed their clinics or had very limited office hours resulted in the 45% of doctors who were not contacted. Despite this design issue the percentages of use were consistent with the findings of the National Board of Chiropractic Examiners (1) as shown in Figure 1.

Conclusion: For the chiropractic physician to provide effective treatment and minimize the risk of harming a patient, yearly calibration and safety checks are essential. This admonition applies not only to ultrasound but also to all forms of therapy in the doctor�s office which utilize electric current.

Very few of the doctors queried during this study recognized the need for yearly calibration checks and electrical safety inspections. These requirements should be emphasized in course work, both graduate and undergraduate. The need for regulatory control is possible if educational emphasis does not improve the failure rate. There are many regulatory agencies present in the arena of healthcare. Compliance checks of x-ray equipment are routinely performed. Medicare has inspectors, as do most State Departments of Health. If chiropractic physicians do not become more aware of their responsibilities in calibration and safety, surely state and national regulatory agencies will.


  1. Christensen MG, editor. Job Analysis of Chiropractic: A project report, survey analysis and summary of the practice of chiropractic within the United States 2000. Greeley, Co: National Board of Chiropractic Examiners; 2000. p. 130
  2. Christensen MG, editor. Job Analysis of Chiropractic: A project report, survey analysis and summary of the practice of chiropractic within the United States. Greeley, Co: National Board of Chiropractic Examiners; 1993. p. 68
  3. Rivest M, Quirion-de Girardi C, Seaborne D, Lambert J. Evaluation of therapeutic ultrasound devices: performance stability over 44 weeks of clinical use. Physiother Can 1987 39(2): 77-86.
  4. Pye SD, Milford C. The performance of ultrasound physiotherapy machines in Lothian Region, Scotland, 1992. Ultrasound Med Biol 1994 20(4): 347-59.
  5. Food and Drug Administration, Code of Federal Regulation, Title 21, Part 1050.10. (4-1-94 Edition).
  6. Bio-Tek Instruments, Inc. Digital Ultrasound Wattmeter: Operator�s Manual. Winooski (VT). August 2000
  7. Bio-Tek Instruments, Inc. Electrical Safety Analyzer: User�s Guide. Winooski (VT). May 1999.
  8. ANSI/AAMI ESI: 1993- Safe current limits for electromedical apparatus. Arlington (VA). Association for the Advancement of Medical Instrumentation. 1993.
  9. Personal correspondence. National Chiropractic Mutual Insurance Company. Statistics for 1996-2000.

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